1. Field of the Invention
The present invention relates to a lens-fitted photographic film unit and to a device for use therewith for changing the size of picture frames to be formed on photographic film by changing the exposure aperture size.
2. Related Art
Recently, many compact cameras having an exposure aperture size changing device have been produced, wherein one of a full-size photography mode and a panoramic-size photography mode may be selected depending on the scene to be photographed, in response to the operation of a photography mode changing member which is accessible from outside the camera body.
In the full-size photography mode, for example, a 24 mm .times.36 mm picture frame of ISO 135 film is provided, and a 89 mm .times.127 mm standard-size photoprint (aspect ratio: 1.5) is made from this ISO 135 full-size frame. In the panoramic-size photography mode, for example, a 13 mm.times.36 mm panoramic-size picture frame is provided, and a 89 mm.times.254 mm panoramic-size photoprint (aspect ratio: 2.8) is made from this panoramic-size frame.
A filmstrip which has been exposed by the above-described camera with frame size changing device may contain full-size frames and panoramic-size frames. When printing such a filmstrip having different size picture frames, it is necessary to adjust the focal length of a printing lens, the size of opening of a paper mask and that of a film mask, and the amount of advance of photographic paper to the frame size. Therefore, in a mini-lab type photographic printer, for instance, a frame size detector consisting of a plurality of photosensors arranged laterally relative to the filmstrip is disposed before a printing gate, so as automatically to determine the size of each picture frame.
On the other hand, lens-fitted photographic film units (hereinafter referred to as film units) are widely used, each of which has a simple exposure mechanism and contains a film cassette so that anyone may enjoy photography with ease. The taking lens of the film unit is comprised of one or two plastic lens elements. Such a taking lens cannot sufficiently correct aberrations such as spherical aberration, curvature of the field, astigmatism and distortion, by improving its own construction. In order to sufficiently correct the aberrations, especially in the peripheral area of the picture frame, the filmstrip is curved to be forwardly and longitudinally concave in an exposure station of the film unit.
If, therefore, an exposure aperture size changing mechanism having conventional flat rectangular masking plates were simply incorporated into a film unit, there would be undesirable gaps between the masking plates and the film surface because of the curvature of the film surface, so that a resulting picture frame would have a barrel shape having convex or outwardly curved top and bottom margins. Such a barrel-shaped picture frame would be hard to detect as a panoramic picture frame with known frame size detectors.
In addition to this problem, an exposure aperture size change mechanism for a film unit should be inexpensive and easy to assemble, in keeping with the inexpensive nature of the film units.
The film units are also required to be as compact as possible. Therefore, the exposure aperture size changing mechanism for a film unit must not greatly increase the size of the film unit. However, the conventional flat aperture masking plates may cause internal reflection and flare spots because an exposure chamber or light-shielding box for the exposure light of the film unit is also of minimize size.